If you want to convert .nrg file to .iso file you can use nrg2iso tool to create this. nrg2iso is a program that extracts ISO9660 data from Nero “.nrg” CD-ROM image files.Install nrg2iso in Ubuntu
sudo apt-get install nrg2iso
Using nrg2iso
Usage
nrg2iso [nrg-file] [iso-file]
Example
nrg2iso image.nrg image.iso
Now you can burn your iso with your preferred linux burning app.